1. Field of the Invention
This invention relates to a process and apparatus for thermal treatment of waste materials using cyclonic combustion which produces low emissions and stable residues. The process and apparatus of this invention provide a very high level of destruction of organic materials in the waste materials while producing a stable, mostly inorganic, vitrified residue having low surface area-to-volume ratios and very low leachability characteristics.
2. Description of the Prior Art
Disposal of waste materials, in particular industrial waste materials, is an ever increasing environmental problem. It is no longer acceptable merely to dispose of raw waste materials in landfills or dumps because many of such waste materials have been shown to create environmental problems, such as by leaching into the surrounding soil, requiring massive clean-up efforts. Numerous processes and apparatuses for disposing of such waste materials are known. The most desirable of these processes and apparatuses produce low emissions into the atmosphere and stabilized residues which can be safely disposed of or, perhaps, subsequently reused for some other purpose.
U.S. Pat. No. 3,926,582, teaches a method and apparatus for pyrolytic treatment of solid waste materials in which solid waste material is charged into the upper region of a pyrolysis chamber and an oxygen-rich gas is charged under pressure into the chamber at a plurality of vertically spaced points along the length thereof to produce combustion of the organic components of the solid waste material and generate heat, producing a plurality of downwardly increasing temperature zones so as to effect incomplete combustion of the organic components and form a combustible gas in the upper zones while melting and oxidizing the inorganic components of the solid waste material into an organic-free molten refractory material in the lower most zone. One disadvantage of this process is the requirement that oxygen-rich gas be employed, thereby adding significantly to the cost of treatment of the solid waste materials. Multi-zone combustion is also taught by U.S. Pat. No. 4,389,979 in which at least a portion of the combustion air required for combustion of fuel is introduced tangentially into the combustion chamber of a stoker-fired boiler. U.S. Pat. No. 4,060,376 teaches a method for combustion of non-gaseous fuels in which the fuel is decomposed in the presence of deficient amounts of primary combustion air to produce a hot combustible gas which is subsequently combusted in secondary and tertiary combustion zones of a furnace and exhausted therefrom. To maintain combustion temperatures below 1400.degree. C. and, thus, control the formation of nitrogen oxides and sulfur trioxides, tertiary combustion air is supplied in more than one stage.
Pyrolysis of combustible solid materials such as waste is taught by U.S. Pat. No. 4,732,091 in which the combustible solid waste material is introduced into the upper section of a pyrolysis chamber and moves downwardly at a controlled rate through multiple stage zones in the pyrolysis chamber, countercurrent to hot gases which are the products of partial oxidation of carbon char occurring at the bottom of a pyrolysis chamber, which hot gases pass upwardly into the pyrolysis chamber.
Cyclonic combustion is taught by U.S. Pat. No. 4,850,288 in which particulate solids are fed tangentially into a primary combustion chamber at its inlet end and flow at high tangential velocity in a helical path through a burner. Oxygen containing combustion gas is supplied tangentially at high velocity through multiple ports spaced along the burner length to maintain and/or increase the high tangential velocity and produce centrifugal forces on the particulate solids, thereby providing for prolonged combustion and high burner volumetric heat release rates. A swirling burner for hot blast stoves having a vertical combustion chamber and an annular blast member located beneath the combustion chamber and provided with a central cylindrical space and a plurality of alternately superposed fuel gas passages and air passages is taught by U.S. Pat. No. 4,054,409.
U.S. Pat. No. 3,744,438 teaches a shaft-type furnace for incineration of refuse materials having a plurality of heating zones in which an essentially non-combustible base mass is charged to the lower zone thereof and heated to molten or semi-molten temperatures, the molten mass providing a high temperature environment in the upper second zone disposed above the lower zone. The refuse material fluid which can be air or a similar fluid which provides support for and/or promotes incineration of the refuse materials are charged into the upper second zone. Non-combustible refuse contained therein drops into the molten mass from which it may easily removed.
U.S. Pat. No. 4,052,265 teaches a process for pyrolytic treatment of waste materials in which the materials are conveyed on a conveyer through a controlled atmosphere treatment chamber without combustion supporting air or other oxidizing agents and caused to progressively thermally breakdown into their more basic constituents which flow out of the material treatment chamber in a continuous liquid and gaseous vapor stream.
Finally, the use of vertical shaft furnaces for treatment of solids in which the solids are generally introduced into the top portion of the shaft furnace or kiln and fall to the bottom through various combustion zones generated within the furnace are taguth by U.S. Pat. Nos. 3,284,915, 3,373,91, 3,250,522, and 3,202,405.